Figure 3.

The Ponzo illusion experiment by Ganel et al. [47]. The top diagram shows the experimental display. Although the rectangular target object located on the right-hand side of the display is perceived as being longer than the one on the left, it is actually shorter. The graph below shows the mean maximum grip aperture and mean perceptual estimations of the participants. Performance when the targets were placed on the Ponzo display is shown on the left and performance when the targets were placed on a control grid with no illusion is shown on the right. Grip aperture was unaffected by the Ponzo illusion and was tuned to the actual length of the target objects. Perceptual estimations, however, were affected by the Ponzo illusion and reflected the perceived not the actual length of the target objects. Adapted from Ganel et al. [47].